Prospective Cohort Study of the Kinetics of Specific Antibodies to SARS-CoV-2 Infection and to Four SARS-CoV-2 Vaccines Available in Serbia, and Vaccine Effectiveness: A 3-Month Interim Report

Abstract

Real-life data on the performance of vaccines against SARS-CoV-2 are still limited. We here present the rates of detection and levels of antibodies specific for the SARS-CoV-2 spike protein RBD (receptor binding domain) elicited by four vaccines available in Serbia, including BNT-162b2 (BioNTech/Pfizer), BBIBP-CorV (Sinopharm), Gam-COVID-Vac (Gamaleya Research Institute) and ChAdOx1-S (AstraZeneca), compared with those after documented COVID-19, at 6 weeks and 3 months post first vaccine dose or post-infection. Six weeks post first vaccine dose, specific IgG antibodies were detected in 100% of individuals fully vaccinated with BNT-162b2 (n = 100) and Gam-COVID-Vac (n = 12) and in 81.7% of BBIBP-CorV recipients (n = 148), while one dose of ChAdOx1-S (n = 24) induced specific antibodies in 75%. Antibody levels elicited by BNT-162b2 were higher, while those elicited by BBIBP-CorV were lower, than after SARS-CoV-2 infection. By 3 months post-vaccination, antibody levels decreased but remained ≥20-fold above the cut-off in BNT-162b2 but not in BBIBP-CorV recipients, when an additional 30% were seronegative. For all vaccines, antibody levels were higher in individuals with past COVID-19 than in naïve individuals. A total of twelve new infections occurred within the first 3 months post-vaccination, eight after the first dose of BNT-162b2 and ChAdOx1-S (one each) and BBIBP-CorV (six), and four after full vaccination with BBIBP-CorV, but none required hospitalization.

Humoral Immune Response Induced by the BBIBP-CorV Vaccine (Sinopharm) in Healthcare Workers: A Cohort Study

“…However, this humoral response diminished progressively between the 90th to 180th day after the second dose, particularly in the NPI group, where lower anti-S-RBD IgG and NAbs were detected than those PI. The seroconverted proportion in the study was comparable but discretely lower than the results reported on phases 1 and 2 of the BBIBP-Corv-2 clinical trials [ 18 ] and other observational studies [ 19 , 20 , 21 ], although higher than that reported by Lijeskic [ 22 ]. However, we did not find a difference in the proportions of seroconverts according to age group, probably because most of our participants were adults under 50 years, and these differences in the humoral response are primarily observed in older patients.…”

Neutralizing Antibody Response to BBIBP-CorV in Comparison with COVID-19 Recovered, Unvaccinated Individuals in a Sample of the Pakistani Population

“…Studies comparing immunogenicity of mRNA vaccines to that of BBIBP-CorV have generally reported lower seroconversion rates and antibody titers in the latter. Lijeskić et al [ 33 ] investigated three vaccines: BNT162b2, BBIBP-CorV, and Gam-COVID-Vac, and observed less potent immune responses in BBIBP-CorV as compared to the other two, while COVID-19 convalescents in this study demonstrated higher titers than BBIBP-CorV, but less than BNT162b2. Petrović et al [ 27 ] similarly reported lower seroconversion rates and antibody titers following BBIBP-CorV than either BNT162b2 or Gam-COVID-Vac.…”

“…Fu et al report 75% seroconversion rate using SARS-CoV-2 RBD ELISA [ 29 ], while Elgendy et al reveal 49% seroconversion, but have tested participants at Day 18 following BBIP-CorV vaccination [ 30 , 31 ]. Alqasseih et al report 85.7% seroconversion at 6 weeks post two-dose BBIBP-CorV vaccine schedule, using a qualitative immunoassay [ 32 ], while Lijeskić et al [ 33 ] have reported 81.7% seroconversion, 6 weeks post-vaccination, using a two-step sandwich enzyme immunoassay method for RBD anti-S antibodies.…”

“…Other studies undertaken on Argentinian and Egyptian health care workers, respectively [ 34 , 35 ], and the general population in Serbia [ 28 ] have also documented prior SARS-CoV-2 exposure increasing BBIBP-CorV post-vaccination antibody titers. Meanwhile, a few studies have also shown that antibody titers following natural infection in unvaccinated individuals are higher than those following BBIBP-CorV vaccination [ 27 , 33 , 36 , 37 ].…”

RBD-specific antibody responses after two doses of BBIBP-CorV (Sinopharm, Beijing CNBG) vaccine

“…This study, however, did find cellular response even with the Sinopharm vaccine. The immunogenicity study from Lijeskić et al reporting data from Serbia [ 49 ] did not find lower antibody response in older subjects, however, the sample size was small.…”